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Re: MIJ Fender Jaguar Bass preamp - schematic and PCB

PostPosted: 14 Oct 2017, 00:21
by george giblet
Re: Schematic and original PCB
I just check this and found a possible bug.

- I did forget to write down the transistor type :slap: :slap: ...
Some 2SCxxxx I can't remember.
[Still don't know. Top view (flat up): BCE]

- The zener diodes (D1 & D2) are BZX85C-5V1

- D3 is a silicon rectifier diode

- Baja: I traced one of these a couple of years back - pretty sure that the emitter resistor on the first transistor is 6k8 not 680 ohms.
[ Correct: Q1 and Q3 all emitter resistors are 6k8; as drawn.]

- Baja: Also the last transistor gain stage should have the 47p capacitor attached between base and ground not the second transistor buffer stage.
[ Incorrect: C10 definitely connects from Q2 base to ground.
The Sadowsky preamp has a cap like this.]

Wire Connections:
A = Treble cw (1)
B = Treble wiper (2)
C = D = Bass cw (1) & wiper (2) and Treble ccw (3)
; no wire actual goes to C, D used for both instead.
E = Bass ccw (3)
F = Emitter of Q3 (not used)

PCB:
C & D connects to C2
E connects to C3 and 18k

So there is something swapped regarding C2 and C3 on the schematic.
Is is the values, the designators or both?
- On the PCB C2 looks like C8, which is 47n.
- From the PCB, C2 connects to C & D (ie. to both bass and treble pots)
We conclude both the designator and values should be swapped
on the schematic. This agrees with the Fender tone stack
cap ratio.